python 3 find in list - python-3.x

Question

I am creating a game and unable to detect turtle position in this list
I am using python3 and turtle.
the objective of this code is to create a filled shape when turtle intersect with its's own path
import turtle
t=turtle.Turtle()
t.fillcolor("red")
t.begin_fill()
s=turtle.Screen()
t.penup()
status=True
penstatus=False
t.speed(1)
x=[]
def go1():
t.left(-(t.heading()))
t.left(90)
def go2():
t.left(-(t.heading()))
# t.left(90)
def go3():
t.left(-(t.heading()))
t.left(270)
def go4():
t.left(-(t.heading()))
t.left(180)
def paint():
global penstatus
if penstatus==False:
penstatus=True
t.down()
else:
t.up()
def detect():
global status
a=t.position()
if a in x:
status=False
print("yes")
while status:
global x
s.onkeypress(go1, "Up")
s.onkeypress(go2, "Right")
s.onkeypress(go3, "Down")
s.onkeypress(go4, "Left")
s.onkeypress(paint,"space")
s.listen()
x.append(t.position())
t.fd(5)
detect()
t.end_fill()
s.mainloop()
it works sometimes but result of filling also gets wrong

Answer 1

There are two reasons you're having trouble detecting if the current position is in your list of past positions. The first is you "hop" five pixels at a time so you are potentially crossing the line at a "filled in" segment, not one you were actually positioned on.
The second is that turtle positions are floating point numbers and can be very slightly different when you come back to the same spot. We can fix both problems by not comparing directly but asking if the distance between points is less than our "hop" distance.
My rework of your code below implements this approach. It also changes how your keys work slightly; changes the logic to only include visible lines in the filled graphic; and is completely event-based. It also has a reset, "r", key to start a new drawing. You can back out any changes you don't like, the back position detection is still applicable:
from turtle import Turtle, Screen
DISTANCE = 3
def go_up():
turtle.setheading(90)
def go_right():
turtle.setheading(0)
def go_down():
turtle.setheading(270)
def go_left():
turtle.setheading(180)
def toggle_pen():
if turtle.isdown():
turtle.penup()
else:
turtle.pendown()
turtle.begin_fill() # ignore pending begin_fill, start anew
def reset_drawing():
global positions
turtle.reset()
turtle.fillcolor('red')
turtle.speed('fastest')
turtle.penup()
positions = []
move()
def move():
for position in positions:
if turtle.distance(position) < DISTANCE:
turtle.end_fill()
return
if turtle.isdown():
positions.append(turtle.position())
turtle.forward(DISTANCE)
screen.ontimer(move, 100)
screen = Screen()
screen.onkeypress(go_up, 'Up')
screen.onkeypress(go_right, 'Right')
screen.onkeypress(go_down, 'Down')
screen.onkeypress(go_left, 'Left')
screen.onkeypress(toggle_pen, 'space')
screen.onkeypress(reset_drawing, 'r')
screen.listen()
turtle = Turtle()
positions = None # make sure global is defined
reset_drawing()
screen.mainloop()